Moving vertices along normal axis in BGE
The vertex normals are the interpolated normals of the faces which are perpendicular to the faces. The vertex normals are normalized this means the length of this vector is 1, therefore you might want to scale them before adding the normal vector to the vertex coordinates.



Moving the vertices along their normals would create an effect as shown in the this image:



import bpy
import GameLogic
###### get the vertex normal vector
# get controller
controller = GameLogic.getCurrentController()
# get object the controller is attached to
obj = controller.owner
# get the 1st mesh
mesh = obj.meshes[0]
for v in range(mesh.getVertexArrayLength(0)):
    vert = mesh.getVertex(0, v)
    norm = vert.normal * .3
    vert.XYZ = (vert.x + norm.x, vert.y + norm.y, vert.z + norm.z )